A sustained increase in arterial blood pressure-i.e. hypertension-is a major cause of excess morbidity and mortality around the world. Chronic arterial pressure levels are thought to be established primarily by the kidney through regulation of total blood volume. The central hypothesis of this project is that veins contribute to long-term control of arterial pressure by actively redistributing blood from high compliance vascular compartments (peripheral, particularly splanchnic veins) to compartments of lower compliance (central veins, heart and arteries). Our goal is to show in intact conscious animals how neurohumoral mechanisms controlling the diameter of peripheral veins (peripheral vascular capacitance) affect arterial pressure and the development of hypertension. We will use two models of hypertension in rats: DOCA-salt;and a new model that we believe is based primarily on venoconstriction, i.e. S6c-induced hypertension. We will address our central hypothesis with the following Specific Aims. 1) Determine if venoconstriction causes body fluid volume redistribution during the development of hypertension by using three complementary methods to assess blood volume redistribution in conscious rats. 2) Establish that one mechanism of decreased vascular capacitance in hypertension is increased sympathetic nerve activity (and/or release of norepinephrine) in the splanchnic region using both direct nerve recording and regional norepinephrine spillover methods. 3) Show how sympathetic innervation to the splanchnic region affects regulation of vascular capacitance and arterial pressure by testing the effects on hypertension development of chronic splanchnic sympathetic denervation, and decreasing elevated superoxide levels in splanchic sympathetic ganglia using gene transfer methods. 4) Determine how venoconstriction ultimately leads to increased arterial pressure by testing the influence of small artery myogenic tone, large artery compliance, and cardiac sympathetic activity on the development of S6c-induced hypertension. Our ultimate objective is to identify novel strategies for treating human hypertension. Lay Summary: High blood pressure (hypertension) is a major human health problem. Many scientists feel the causes of hypertension can be found in abnormal function of the kidney or arteries. This project tests the idea that altered structure or function of veins also may cause hypertension, and that it may be possible to treat hypertension using drugs that affect veins.